The purpose of this study is to measure the basement membrane thickness in diabetic and control parietal yolk sac (11.5, 13.5 and 15.5 day mothers and their respective embryos). We are using 6 mothers, 6 embryos per mother, and 4 blocks per embryo. From this, 15 over-lapping photographs are taken and combined into a photomontage covering 75 cm in order that the basement membrane thickness at 15 points (5 cm apart) may be measured. We have finished the study of the 13.5 day animals. The results for average blood sugar levels are: Controls: 160 mg/100 ml plus or minus 35; Diabetics: 680 mg/100 ml plus or minus 165. The results for mean thickness of basement membrane are: Controls: 3.104 microns plus or minus 0.68; Diabetics: 3.141 microns plus or minus 0.96. Since the latter data is not statistically significant, if no significant difference is found in the 11.5 and 15.5 day animals, the implication would be that basement membrane synthesis and secretion in diabetic animals can proceed along normal lines; however, if a difference is found, a suitable model for studying abnormalities of basement membrane synthesis and secretion in a system that turns over fast enough to allow for experimental manipulation would be provided. In this year of our study, we shall complete the photography and the measurement and statistical analysis for the 11.5 and 15.5 day animals. Sectioning for electron microscopy is almost complete.